The invention relates to filling valves for pressure refueling devices of the kind comprising a hollow body having an annular passage between upstream connection means and downstream connection means; the passage having a seat co-operating with a movable closure unit, wherein the body is provided with axially guiding means for the closure unit which are substantially fuel-tight so that the unit limits two chambers, i.e. an outer chamber forming part of the annular passage and an inner chamber permanently communicating with the upstream connection means and adapted to be connected by control means to a discharge or exhaust duct. The invention more particularly relates to such valves in which the pressure of the fuel acting on the wall of the closure unit limiting the outer chamber tends to open the shut-off means (i.e. to move it away from its seat), whereas the pressure of the fuel acting on the wall of the shut-off means limiting the inner chamber (which pressure possibly is supplemented by the action of resilient return means) tends to close the closure unit, and the resulting force exerted in the opening direction is greater or less than the force exerted in the closing direction depending on whether the exhaust duct is freed or not by the control means.
Filling valves of the aforementioned kind are used for filling fuel tanks in general, more particularly vehicle and typically aircraft tanks.
As is known modern aircraft, more particularly jet planes and especially planes having a high capacity, represent an extremely large investment by the air companies using them. In order to pay off them as economically as possible, the companies have to operate with high working ratios necessitating very short dead times at stop-overs, i.e. refueling at very high flow rates, which can be done only by using pressure filling circuits.
Such circuits usually comprise one or more fuel intakes for removably receiving to the inlet pipes for providing fuel under pressure and piping for distributing the fuel between the various aircraft tanks, and are provided with suitable accessories such as taps and valves. Furthermore, each tank or group of tanks comprises a filling valve of the aforementioned kind. The control means can be actuated by any suitable signals, usually electric or hydraulic signals, which are emitted either manually or automatically by a suitable device such as an electric contact level, a float needle or the like. The filling valves are intended to stop the filling operation when the tank is full and also to protect it against transient excess pressure (water-hammer effect) or permanent excess pressure due to the faulty action of the fuel-distributing devices on the ground.
Usually the filling valve is closed if there is no pressure in the upstream connection or if there is a pressure but the control means are out of action. In order to open the valve, the pressure in the inner chamber is reduced to the value of the downstream pressure or to a value intermediate between the upstream and downstream pressures, by opening the exhaust duct. As soon as the required level has been reached in the tank, the exhaust duct is again closed, thus restoring the initial pressure in the inner chamber which, in conjunction with resilient return means if required, closes the filling valve.
Existing filling valves have the drawback that they provide very little or no protection to the tanks against excess pressures. If, therefore, the upstream pressure permanently increases, the flow rate through the valve increases and the vents from the tank to atmosphere may become insufficient, thus producing dangerous excess pressures in the tank.
It is an object of the invention to provide fueling valves which protect the tanks to which they are connected against excess pressures.
A valve according to the invention comprises means responsive to the flow rate of fuel through it and which are adapted to increase the ratio between the fuel pressure in the inner chamber and the fuel pressure in the outer chamber in proportion as the flow rate increases. The means responding to the flow rate may comprise a movable sleeve guided in the body parallel to the flow direction of fuel in the body, the means being provided with a driving surface disposed transversely with respect to the fuel flow direction and acted upon by resilient means in the direction opposite to the flow direction.
In a first embodiment, the means responding to the flow are actuated so as to increase the fuel pressure in the inner chamber in proportion as the flow rate increases. If the means comprise the aforementioned movable sleeve, the sleeve can be actuated so as to increase the cross-section through which the upstream connection communicates with the inner chamber or to decrease the cross-section through which the inner chamber communicates with the downstream connection, in proportion as the flow rate increases.
According to a second embodiment, the means responding to the flow rate are actuated so as to decrease the fuel pressure in the outer chamber in proportion as the flow rate increases. If the aforementioned means comprise the aforementioned sleeve, the sleeve can be actuated so as to produce a pressure drop which increases with the flow rate in the annular passage.